N-Phosphonomethylglycine and certain salts are particularly effective as a post-emergence herbicide. The commercial herbicide is sold as a formulation containing the isopropylamine salt of N-phosphonomethylglycine.
N-Phosphonomethylglycine can be made by a number of methods. One such method, as described in U.S. Pat. No. 3,160,632 is to react N-phosphinomethylglycine (glycinemethylenephosphonic acid) with mercuric chloride in a water solvent at reflux temperature, and subsequently separating the reaction products. Other methods are phosphonomethylation of glycine and the reaction of ethyl glycinate with formaldehyde and diethylphosphite. The latter method is described in U.S. Pat. No. 3,799,758. In addition, there is a series of patents relating to the preparation of N-phosphonomethylglycine, including U.S. Pat. Nos. 3,868,407, 4,197,254 and 4,199,354.
Close prior art is U.S. Pat. No. 3,923,877, which teaches the reaction of PhCH.sub.2 NHCH.sub.2 C(O)OH with H.sub.3 PO.sub.3 and HCHO in dilute HCl at reflux to form (HO).sub.2 P(O)CH.sub.2 N(CH.sub.2 OH)CH.sub.2 C(O) followed by refluxing in aqueous HBr to yield N-phosphonomethylglycine.
Because of the commercial importance of N-phosphonomethylglycine and certain salts as a herbicide, improved methods of preparing these compounds are valuable.